1) As long as you have enough memory, any processor should work (it may take a while though).
2) I assume you mean 3GB, right? A 32-bit OS genrally runs out of address space at 4GB. You simply can't "count" any higher. For anything more, you'd have to eplicitly store things to disk, and that will slow things down.
4) The viewer is able to make use of higher-end graphics cards, so the experience should be better. There should be no difference for the synther.